The present invention relates to a coordinate input apparatus having a projection display section for irradiating a coordinate input screen with light from a pointing device to generate a light spot, generating coordinates corresponding to the light spot, and displaying an image on the coordinate input screen, a control method therefor, and a computer-readable memory.
Conventionally, a coordinate input apparatus which senses a light spot on a screen using a CCD area sensor or linear sensor, executes image processing using, e.g., barycentric coordinates or pattern matching, and calculates and outputs coordinate values, or a coordinate input apparatus using a position detection element (an analog device capable of obtaining an output voltage corresponding to the position of a spot) called a PSD is known.
For example, Japanese Patent Publication No. 7-76902 discloses an apparatus which senses a light spot formed by a parallel beam of visible light with a video camera to detect coordinates and simultaneously transmits/receives a control signal by infrared diffused light. Japanese Patent Laid-Open No. 6-274266 discloses an apparatus for detecting coordinates using a linear CCD sensor and special optical mask.
Japanese Patent No. 2,503,182 discloses the arrangement of an apparatus using a PSD and an output coordinate correction method for the apparatus.
A recent wide-screen display is increasing in screen size and resolution as well as in brightness. Hence, the resolving power of a coordinate input apparatus must also be improved.
Conventionally, a coordinate input apparatus of this type has, as main components, a pointing device for forming a light spot on a screen serving as a coordinate input surface and a coordinate detector for detecting the coordinate position of the light spot on the screen, and additionally as an output device, a projection display device which displays an image or coordinate position on the screen, as described in Japanese Patent Laid-Open No. 11-219253. A compact and inexpensive apparatus which uses a ring CCD as a coordinate detector and is resistant against disturbance light has been proposed.
In this coordinate input apparatus, a cylindrical lens or the like is laid out in front of the ring CCD, thereby inputting light incident on the entire input screen to the ring CCD.
For example, light components input to the same X-coordinate are input to CCD pixels linearly arranged along the X-axis through different paths depending on the position. At this time, the imaging position or input light intensity distribution changes depending on, e.g., the aberration of the lens or a variation between individual lenses. This may cause an error in coordinate values detected by the CCD pixels. Instead, when CCD output values of a plurality of known coordinate points on the screen are stored in a nonvolatile memory, and coordinates are calculated on the basis of the CCD output values, the accuracy can be improved.
Additionally, in the coordinate input apparatus of this type, since the screen size can easily be changed by changing the distance between the projection display device and the screen, the screen size may be changed by user option after shipment from the factory.
In this case, no problem is posed when the optical axis of the projection display device of the coordinate input apparatus matches that of the coordinate detector. However, if the optical axes do not match, the coordinate calculation using the CCD output values stored in the nonvolatile memory generates a considerable deviation in coordinate values.
The present invention has been made in consideration of the above problems, and has as its object to provide an accurate coordinate input apparatus, control method therefor, and a computer-readable memory.
According to the present invention, the foregoing object is attained by providing a coordinate input apparatus which detects light from a pointing device, with which a coordinate input screen is irradiated, by a coordinate detector, thereby generating a coordinate output signal corresponding to a position on the coordinate input screen, which is irradiated with the light, comprising: storage means for storing a plurality of coordinate values corresponding to outputs from the coordinate detector which are obtained by irradiating a plurality of predetermined positions on the coordinate input screen with the light; selection means for selecting coordinate values from the plurality of coordinate values stored by the storage means; and arithmetic means for calculating the position on the coordinate input screen, which is irradiated with the light, on the basis of the selected coordinate values.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.